Connectivity in Challenged Environments: Mobile connectivity has become so pervasive that humanity takes it for granted similar to a basic utility like electricity or water. However, making this utility available to a significant chunk of the world's population in several developing and rural parts of the world, is still not economically viable. In addition, even in places, where such a connectivity infrastructure exists, one cannot completely rely on it in times of natural calamities and disasters, where it can be significantly compromised. With recent advances in un-manned aerial vehicle (UAV) technology, one can envision aerial connectivity infrastructures that can be deployed and torn down "on-demand". This provides a game-changing option in these challenging environments, especially for public safety scenarios, and serves as a useful complementary connectivity modality in other hot-spot scenarios like events, venues, etc. The goal of this project is to design and deploy an end-to-end system that addresses the various technical challenges in the deployment of a network of low-altitude UAVs that can provide optimized LTE connectivity over a desired geographic region.

• SkyLiTE: A self-organizing network of low-altitude UAVs that aim to provide optimized LTE connectivity in a desired region

Network densification, i.e. making the communication cells smaller and denser in deployment, can allow for aggressive reuse and scaling of spectral resources, thereby providing a potential solution for the "capacity crunch" problem. However, realizing this in practice faces several fundamental challenges. We have designed and prototyped novel solutions for addressing the challenging problem of "pervasive interference" in small cells - our solutions intelligently leverage resources from multiple dimensions (time, frequency and space) effectively. Some of our system related efforts in this area include

• ProBeam, iBUS: Practical single-cell and multi-cell beamforming systems for LTE small cell networks

• RADION: A distributed resource and interference management system for small cells

• FERMI: A centralized resource and interference management system for small cells

Spectrum Access Management, i.e. the ability to utilize the scarce spectral resources efficiently, is an integral component in the efficient operation of wireless networks. Challenges arise when this has to be accomplished in the face of heterogeneity arising from access modalities (eg. base station-client vs. peer-peer) and technolgies (LTE vs. WiFi) that operate complementarily (through offload) or in competition (e.g. LTE-U, LTE-LAA, CBRS), where they vye for the same resources. Our works in this space include

• BLU: A system that blue-prints un-known interference to enable robust LTE access in unlicensed spectrum

• ULTRON: Efficient Co-existence of LTE with WiFi in un-licensed spectrum

• ATOM: Adaptive traffic mangement/offloading solution using LTE and WiFi for mobile networks

• R2D2: LTE Device-Device communication as a flexible offloading mechanism for improved spectrum utilization

For more information on our small cell projects, please check here.

Smart antennas are extremely vital to the performance of a wireless network. They can deliver promising gains within a single cell as well as reduce interference between cells. Over the past decade, they have evolved from simple switched beamforming antennas to sophisticated multiple-input multiple-output (MIMO) techniques, multi-user MIMO (MU-MIMO) and more recently wireless full-duplex and mmWave technologies. However, leveraging these technologies effectively requires intelligent higher layer solutions that (i) are smart antenna aware, and (ii) can scale their benefits to a large network of cells without incurring prohibitive measurement overhead. We have designed and built novel solutions with these attributes for various forms of smart antenna techniques, including the more recent network MIMO, full-duplex and mmWave systems. Some of our recent systems in this domain include

• Hekaton: A dual- layer beamforming system for large MIMO arrayswith reduced measurement and energy overhead

• MIDAS: Empowering 802.11ac (multi-user MIMO) networks with multiple-input distributed antenna systems

• NEMOx: A system for leveraging network MIMO gains in a scalable manner in large wireless networks

• ADAM: A system for improving wireless link layer multicasting with the use of adaptive beamforming antennas

• FDoS: Enabling wireless full-duplex communication between full-duplex access points and legacy half-duplex clients

• MIDU: A system that enables tandem operation of MIMO and Full Duplex, with a judicious use of available spatial degrees of freedom between them

• SpaceBeam: A one-shot (zero overhead) mmWave beam configuration system that leverages IR-Lidar (available on autonomous platform agents in industrial and automotive) to infer scene geometry that is relevant for RF mapping in mmWave frequencies.

For more information on our projects in these smart antenna areas, please check here.